Published 6:00 pm, Wednesday, February 6, 2008

Cornyn said he told his Arizona colleague by phone that he was backing him.

Cornyn, who is running for re-election, announced the endorsement after McCain's chief rival, Mitt Romney, suspended his campaign. Cornyn's backing could help McCain as he tries woo conservatives to back him. Cornyn is a conservative who is part of the Senate leadership.

Cornyn gave McCain his support despite a public shouting match with him last year that was widely reported.

The two argued in a closed door meeting while putting the final touches on a comprehensive immigration bill.

Cornyn was unhappy with details of the proposal. When McCain cursed at him for raising his concerns, Cornyn responded by complaining that McCain had been neglecting the negotiations to campaign for president. McCain responded with another expletive, according to media reports about the exchange.

"Although I've had some differences with Sen. McCain over time, that's really not unique to him. It's the nature of our political system where people have disagreements on various matters," Cornyn said.

Cornyn said McCain is the best presidential candidate, Republican or Democrat, on issues that matter most to him _ national security and wasteful spending.

McCain issued a statement thanking Cornyn for the support.

The two took different approaches on immigration. McCain crafted bills that would have allowed illegal immigrants to remain in the U.S., work and eventually gain legal residency. Cornyn wanted immigrants to return to their home country before returning to work legally or seek U.S. residency.

Sen. Kay Bailey Hutchison has not endorsed a candidate.

Texas Gov. Rick Perry initially endorsed former New York Mayor Rudy Giuliani but switched to McCain the day after Giuliani dropped out of the race.